Edinburgh Napier University

  Ensuring that predicted (simulated) energy performance figures are realised once a building is in-use has been of growing concern since issues surrounding the ‘performance gap’ were realised in the mid 1990’s [1]. Increasing energy demand and a decrease in thermal comfort with an added pressure on fuel poor occupants has questioned why some dwellings are not delivering their design expectations.
In accordance with the Energy Performance of Buildings Directive (Directive 2010/31/EC,EPBD) [2], each EU member state is required to evaluate at design stage the energy performance of buildings. Following these predictions, it is expected that the completed building is constructed to a performance level which ultimately reflects the design model. There is, however, significant evidence to show that buildings are not achieving these aspirational energy requirements which often translates into higher energy bills for the occupant(s).
This paper has evaluated the difference in energy demand at the design stage and early-occupation stage of two similar dwellings constructed in Scotland for a large social landlord. The dwellings were constructed side-by-side, built using a similar timber frame system fabricated by the same manufacturing firm. One dwelling was constructed to Passive House (Passivhaus) standards, the other in accordance to conventional 2010 Scottish Building Regulations. Furthermore, this paper presents in-situ thermal envelope evaluation results that were measured at post-construction and early occupation stage.
The early findings from this research have shown that energy figures obtained through real-time hourly data of space and water heating for the Passive House and the more conventionally designed house during the first year of occupation were 37% and 35% higher in energy consumption, respectively, than the predicted figures. Field test results have provided evidence to suggest that this increased demand is, in-part, due to some deficiencies of the thermal envelope. Other factors that influence the operation of the dwelling, for example building services efficiency, control systems and occupant behaviour have also contributed to widening the performance gap.